Vehicles, such as automobiles, may include a steering system operable by a driver of the vehicle to alter a direction of travel of the vehicle. Such a steering system may include a power assist unit configured to reduce the effort that must be applied by the driver to a steering control (e.g., a steering wheel) to achieve a change in direction of the vehicle. Various conditions may compromise the directional stability of the vehicle, may require the driver to make incremental or constant corrections to the direction of travel of the vehicle, and/or cause feedback through the steering wheel. Deviation from a desired path of travel may be referred to as “drift,” and undesirable feedback through the steering wheel may be referred to as “pull.” For example, crowned roads or strong crosswinds may temporarily cause diversion from the intended path of the vehicle. Additionally, misalignments of the vehicle steering and/or suspension components, side-to-side variations in tire inflation pressure, or other mechanical factors may cause the vehicle to pull to one side even when the driver intends to follow a straight direction of travel. Power steering systems may be configured to apply steering assist force to reduce (e.g., eliminate) drift and pull.
The directional instability due to factors such as road crown and/or crosswinds may change rapidly due to changes in road surface and environmental conditions, and the directional instability due to factors such as chassis misalignment or inconsistent tire inflation generally will not change with changes in road surface or environmental conditions. It may be desirable to separate the components of directional instability due to road surface and environmental factors from components of directional instability due to vehicle factors to enable more consistent compensation and steering feel.